1. Field of the Invention
The present invention relates to a pulley unit having a one-way clutch. This pulley unit can be provided in, for example, an auxiliary machine driven through a belt by a crank shaft of a vehicle engine. The auxiliary machine may include, for example, an alternator, air conditioner compressor, water pump, cooling fan of a vehicle and the like.
2. Description of the Related Art
Various auxiliary machines mounted on a vehicle engine are driven through a belt by a crank shaft of its engine. In case of an alternator, for example, which is one of the auxiliary machines, if it is coupled with an engine crank shaft so as to rotate synchronously therewith, power generation capacity of the alternator decreases if the rotation speed of the crank shaft drops.
Thus, the inventor of the present invention has considered that by incorporating a one-way clutch in the alternator, the rotation of a rotor of the alternator is kept the same by its inertia force if the rotation speed of the crank shaft drops, thereby improving power generation efficiency.
That is, a one-way clutch is disposed between a pulley and rotor of the alternator and the one-way clutch is changed between a locking state (driving power transmission state) and a free state (driving power transmission shut-down state) depending on a difference of rotation speed between the pulley and rotor so as to transmit the driving power or shut down transmission thereof between the pulley and rotor. To smooth a relative rotation of the pulley and rotor, and reduce the load, the rolling bearings are disposed on both sides of the one-way clutch.
According to the above conventional example, when the pulley is driven by a belt wound on an outer periphery thereof, a radial load from the belt is applied to the one-way clutch and rolling bearings on both sides. In this condition, by the a radial load from the aforementioned belt, the tightening distance between the pulley and outer wheel of the one-way clutch is increased so that the outer wheel of the one-way clutch becomes likely to be distorted. Consequently, the dimension in the diameter direction of the wedge-like spaces provided on several positions along the circumference of the one-way clutch is reduced so that the rollers are displaced to the free side. As a result, a wedge angle of the wedge-like space becomes likely to be reduced. If the wedge angle becomes smaller than its lower limit value, the roller of the one-way clutch remains locked but is not made free. That is, the proper functioning of the one-way clutch is lost.
Because usually, the belt is applied to a partial range of the pulley within a predetermined angle range of the circumference thereof, the aforementioned distortion of the outer wheel is not generated equally on the entire circumference but partially. Therefore, it can be considered that the aforementioned problem is induced by some of the plural rollers provided on the one-way clutch.
Although, according to the conventional art, the tightening distance between the pulley and one-way clutch or rolling bearing needs to be set large for the one-way clutch or rolling bearings on both sides not to slip out of the pulley in the axial direction due to a vibration, if the tightening distance is set larger than an appropriate one, the dimension in the diameter direction of the wedge-like space is reduced so that the wedge angle becomes small. Consequently, the proper functioning of the one-way clutch is lost. Therefore, according to the conventional art, a sufficient tightening distance between the pulley and one-way clutch cannot be ensured so as to prevent a slipout thereof.